Automotive Internal Combustion Engine Cutaway Step 2 - The engine begins by pulling air through the air intake throttle actuator which is controlled via the computer, and foot actuator that is located in the drivers compartment. This air flow is monitored by the mass air flow sensor and cleaned by the air filter.
Electronic Throttle Actuator Step 3 - Once air has passed through the throttle actuator, it enters the intake manifold were it is divided among individual cylinder intake ports.
Intake Port Cutaway Step 5 - Fuel enters the intake port or directly into the combustion chamber via a fuel injector which is controlled by the computer.
Port Fuel Injector Step 6 - A camshaft is used to open each valve while it rotates as the engine is operating. A spring returns the valve to the closed position which is called a "valve spring". (Overhead camshaft configuration shown.)